1. Field of the Invention
This invention relates to video memories.
2. Description of the Prior Art
A digital video tape recorder (DVTR) uses a video memory to store video data replayed from a digital video tape.
In a previously proposed DVTR, replayed video data comprising a succession of so-called `inner` data blocks are first subjected to an initial `inner` stage of error correction. Inner error correction is performed on individual inner data blocks to correct replay errors of up to a certain severity and to detect (but not to correct) more severe replay errors. Any replay errors in an inner data block which are detected but uncorrected by the inner error corrector are signified by an error flag output by the inner error corrector and associated with that inner data block.
The output from the inner error corrector, i.e. the inner data blocks with their associated error flags and other ancillary data such as a video field identifier, are then stored in a video memory or field store. The contents of the video memory are then read out in a transposed order as `outer` data blocks comprising individual pixel data words from a predetermined sequence of inner data blocks, for a further stage of error correction by an `outer` error corrector. In order that the data in the video memory can be read out in a different order to that in which they were stored, the error flag and other ancillary data associated with each inner data block are stored with each individual pixel data word in that inner data block. For example, if the pixel data words in the inner data blocks each comprise 8 bits and there are 4 bits of ancillary data associated with each inner data block, then the above arrangement will mean that the video memory has to store 12-bit data words so that each data word contains the video data and the ancillary data associated with the inner data block of that pixel data word.
The provision of a 12-bit wide video memory to store the 8-bit pixel data words means that a wider data bus and additional buffering and associated components are required. This adds to the complexity and physical size of the replay processing apparatus in a DVTR.